The hazards of eating leftovers for a long time include affecting appetite and increasing the risk of gastrointestinal diseases, as follows. 1. Impact on appetite: leftovers generally color, traits, etc. will change, such as green vegetables from bright green to yellow-green or even yellow, in addition, the taste may also become worse, thus affecting the desire to eat. 2. Increase the risk of gastrointestinal diseases: improper preservation of leftovers is extremely easy to breed bacteria, long-term consumption will lead to a large number of bacteria into the gastrointestinal tract, resulting in abdominal pain, diarrhea and other discomforts, and in severe cases, even induce gastrointestinal tract tumors. Therefore, it is not recommended to eat leftovers for a long time, should be cooked on demand. In addition, when eating leftovers, be sure to heat them sufficiently.